The pair of oxides, which can be leached out, when powdered bauxite containing certain impurities is…
The pair of oxides, which can be leached out, when powdered bauxite containing certain impurities is digested with concentrated solution of $\mathrm{NaOH}$ at $473-523 \mathrm{~K}$ temperature and $35-36$ bar pressure are
Bauxite is the most important ore of aluminium contains only $30-60 \% \mathrm{Al}_2 \mathrm{O}_3$, the rest being a mixture of $\mathrm{SiO}_2, \mathrm{Fe}_2 \mathrm{O}_3$ and $\mathrm{TiO}_2$. The powdered bauxite is treated with concentrated solution of $\mathrm{NaOH}$ resulting in the dissolution of $\mathrm{Al}_2 \mathrm{O}_3$ and $\mathrm{SiO}_2$ while the other oxides $\left(\mathrm{Fe}_2 \mathrm{O}_3\right.$ and $\mathrm{TiO}_2$ ) being basic remain insoluble in $\mathrm{NaOH}$. Hence, only $\mathrm{SiO}_2$ and $\mathrm{Al}_2 \mathrm{O}_3$ leached out.